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Abstract

The 2004 Indonesia tsunami as well as the increasing storm frequency and intensity associated with climate change–sea-level rise have highlighted the coastal protection function, among the many goods and services that mangrove forests provide. This wider awareness of mangroves has increased national and international rehabilitation efforts, given only 15 million ha remaining and yearly rates of 1–3% loss. Rehabilitation programs employ two strategies: seafront planting and pond reversion. Seafront planting is necessary because coastal populations will not move to safer ground by choice, or cannot move due to poverty, and is also preferred because the sites are open access with no tenurial conflicts. However, former sites of fringing mangroves are difficult to rehabilitate as their lower intertidal–subtidal levels are not optimal for mangroves (due to frequent inundation and wave action). Planting in tidal flats and seagrass beds is also ecologically misguided. This chapter evaluates the relevant mainstream and gray literature (on site and species selection, propagule sources, nursery protocols, outplanting techniques, biophysical/anthropogenic threats, and novel interventions, e.g., integrated approaches using barriers) to improve the low survival rates of seafront planting. However, this strategy should not preclude the long-term relocation of coastal communities to safer ground and the politically difficult option of pond reversion. Given thousands of hectares of underutilized and abandoned brackish water ponds in Southeast Asia, this option holds greater potential for rehabilitation of wide areas of mangroves and greater species diversity. It is ecologically easier as it merely requires restoring hydrology (by breaking pond dikes); mangrove recruitment and succession naturally follow (if propagule sources are present) in these ponds located at mid-upper intertidal levels where mangroves naturally occur. The Philippines, with its long history of mangrove–pond conversion and problematic enforcement of laws that mandate mangrove reversion of idle ponds, is examined as a case study. The chapter assesses the Fishpond Lease Agreement (FLA) system by which vast expanses of mangroves were transferred from the public domain (government-leased ponds) to private ownership and recommends ways to improve the FLA system.

A total of 4845 penaeids belonging to nine species—Metapenaeus anchistus, M. ensis, M. moyebi, M. philippinensis, Penaeus merguiensis, P. monodon, P. semisulcatus, P. latisulcatus and Metapenaeopsis palmensis—were collected by pocket seine monthly over 13 months from mangrove and non-mangrove sites in Guimaras, Philippines. The restricted distribution of the three dominant species—M. ensisandP. merguiensisto the brackish water riverine mangrove, andM. anchistusto the high-salinity island mangrove and tidal flat—is probably related to different salinity and substrate preferences. Abundance and size composition of the major species suggest a strong nursery role for the riverine mangrove (high juvenile densities, relatively small sizes year-round), limited nursery use of the island mangrove (fewer shrimps, larger size ranges, presence of maturing females) and a non-nursery use (e.g. foraging) in the tidal flat. Penaeid recruitment to the river had two peaks in November and May when the average salinity was ∼20 (Practical Salinity Scale) and water temperatures were high (30–31 °C). The spatio-temporal pattern of penaeid species in Guimaras shows partitioning across habitats and seasonal recruitment influenced by physical and biological factors.

The proceedings have three review papers on the mangroves of Southeast Asia, silvofisheries, and Indonesia's integrated mangrove forest and aquaculture systems. The rest of the papers, all on mangrove-friendly aquaculture efforts are from the Philippines, Japan, Thailand, Vietnam, Malaysia, Brunei Darussalam, Indonesia, and Cambodia. All the countries represented had varied methodologies, with Cambodia in its initial stages while some countries like Indonesia and Thailand have tested methodologies. The proceedings include a tabulation of the reported mangrove-friendly technology by country -- e.g. silvofisheries in ponds (mangrove and fish/shrimp/mudcrab) and pens (mangrove and mudcrab). The workshop recommendations are classified into three major topics: problems associated with mangroves, problems associated with aquaculture practices, and socioeconomic and cultural issues.

Although multilateral agencies in Southeast Asia have long been promoting that mangroves, and other wetlands, are wastelands to be put into better use, such as conversion to ponds. However, there is a need for Mangrove Friendly Aquaculture (MFA) technology in the intertidal forest, or swamp, which does not require the clearing of trees. MFA may be defined on 2 levels: 1) silvofisheries or aquasilviculture, where the low density culture of crabs, shrimps and fish is integrated with mangroves; and, 2) mangrove filters where mangrove forests are used to absorb the excess nutrients in the effluents from high-density culture ponds. A review is made of MFA practices belonging to the first category. Discussion is on a country basis, moving from traditional systems in Indonesia, to the introduced technologies in Indonesia, Vietnam, the Philippines and Malaysia. It is hoped that this review will be of use to scientists, aquaculturists, policy makers and governmental/NGOs interested in making aquaculture more ecologically sound and socially responsible.